This invention relates to stable latexes of chloroprenealpha, beta-unsaturated carboxylic acid copolymers, prepared by the polymerization of the corresponding monomers in the presence of protective colloids.
The prior art has been mainly directed toward incorporating nonionic surfactants and protective colloids as a postpolymerization addition to a conventional soap stabilized latex, or during polymerization in conjunction with a predominant amount of conventional surfactant.
German Offenlegungsschrift No. 2,426,012 disclosed the preparation of stable polychloroprene latexes by the polymerization of systems substantially free of the soaps of long-chain fatty acids and rosin acids and comprising the chloroprene monomer with polyvinyl alcohol and dialkyl xanthogen disulfide or alkyl mercaptan chain transfer agents and optionally with copolymerizable alpha, beta-unsaturated short chain carboxylic acids. The latexes are disclosed to be useful as adhesives, which may be highly loaded with eletrolytes and other materials commonly included in latex formulations and remain stable whereas the fatty acid and rosin soap stabilized latexes would coagulate.
Latexes made in systems without anionic or cationic soaps or surfactants are made to fill a need for a polychloroprene latex which will remain stable over a wide pH range and when large amounts of fillers, electrolytes and other compounding ingredients are added, without a corresponding large amount of surface active agents.
In particular, the latexes of the present invention can be heavily loaded with electrolytes (ionic material) which would immediately coagulate conventional surfactant stabilized emulsions. Such electrolytes include aluminum hydroxide, antimony chloride, zinc oxide, magnesium oxide and the like. Polychloroprene, which is heavily loaded with such materials has high flame retardant properties. The electrolyte loaded latexes may be foamed by known methods, dried and applied over highly combustible polyurethane foams used for cushions, padding, mattresses and the like to provide a foam composition which has vastly improved flame retardant properties.
It is an advantage of this invention that emulsion polymerization of chloroprene and a small amount of lower acid comonomer may be carried out without long chain fatty acid or rosin acid soap emulsifiers. It is a further advantage that shorter polymerization times and better controlled polymerizations are obtained over polyvinyl alcohol as the sole protective colloid. It is a still further advantage of the present invention that smaller amounts of polyvinyl alcohol may be used than possible previously, to achieve a higher degree of latex stability. These and other advantages will become apparent from the following: